1) Field of the Invention
The invention relates to redispersible tackifier powders and to adhesives which comprise redispersible tackifier powders in powder form or in the form of their aqueous redispersion.
2) Background Art
Use as adhesives is an important area of application for polymers, for example homopolymers or copolymers of vinyl esters, (meth)acrylic esters or styrene. An example of this is the use of vinyl acetate-ethylene copolymers as flooring adhesives (EP-A 23360, U.S. Pat. No. 4,322,330). EP-A 620243 describes the use of vinyl ester-acrylate copolymers as contact adhesives or flooring adhesives. DE-A-3737630 (U.S. Pat. No. 4,975,481) relates to contact adhesives which are based on ethylene-vinyl acetate copolymers. EP-A 17986 (U.S. Pat. No. 4,322,516) disclosed contact adhesives based on acrylate-vinyl acetate-ethylene copolymers. EP-A 490191 (U.S. Pat. No. 5,196,468) relates to the use of aqueous acrylate latices as flooring adhesives. In the applications mentioned these polymers can in principle be used in the form of their powders or aqueous dispersions.
Especially for use as contact adhesives or flooring adhesives, the addition of tackifying substances, tackifiers, including tackifier resins, is often necessary in order to improve the tackiness. These tackifiers can be added to the aqueous dispersion as a solution in plasticizer (EP-A 23360). DE-A-3737360 discloses the addition of the tackifier to the polymer dispersion as a solution in organic solvent or in the form of its melt. EP-A 490191 describes a procedure in which a melt of tackifier resin and surface-active substances is added to the adhesive dispersion. In EP-A 620243, an aqueous suspension of the tackifier resin is added to the adhesive dispersion.
In the case of the tackifier solutions, a disadvantage of these procedures is the release of the volatile solvent during or after processing. Adding tackifier resins in the form of the melt is a time-consuming and energy-intensive process step which makes the production of the adhesive more expensive. When aqueous tackifier dispersions are added, there is a normally unwanted dilution of the adhesive dispersion. Moreover, it is not possible without taking additional steps to mix aqueous tackifier dispersions homogeneously with adhesive powder.
The object was therefore to provide a tackifier composition which can be used to modify both pulverulent and aqueous adhesives without the abovementioned disadvantages occurring.